update cosign to 2.0.0 and builder image and also cosign flags

[cpanato]

Summary

• update cosign to 2.0.0 and builder image and also cosign flags

[codecov]

Codecov Report

Merging #1368 (2ada9aa) into main (aaf3e5f) will increase coverage by 16.29%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             main    #1368       +/-   ##
===========================================
+ Coverage   47.81%   64.10%   +16.29%     
===========================================
  Files          82       82               
  Lines        7906     7906               
===========================================
+ Hits         3780     5068     +1288     
+ Misses       3420     2184     -1236     
+ Partials      706      654       -52     

Flag	Coverage Δ
e2etests	47.81% <ø> (ø)
unittests	42.65% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/types/entries.go	52.54% <0.00%> (+1.69%)	⬆️
pkg/api/index.go	69.29% <0.00%> (+1.75%)	⬆️
pkg/pki/factory.go	83.33% <0.00%> (+1.85%)	⬆️
cmd/rekor-cli/app/search.go	57.85% <0.00%> (+2.14%)	⬆️
pkg/types/jar/v0.0.1/entry.go	56.54% <0.00%> (+3.73%)	⬆️
pkg/util/validate.go	100.00% <0.00%> (+3.92%)	⬆️
pkg/pki/ssh/encode.go	54.71% <0.00%> (+5.66%)	⬆️
pkg/types/intoto/v0.0.2/entry.go	66.23% <0.00%> (+9.00%)	⬆️
pkg/types/tuf/v0.0.1/entry.go	61.02% <0.00%> (+10.23%)	⬆️
pkg/types/helm/helm.go	37.03% <0.00%> (+11.11%)	⬆️
... and 31 more

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